The present invention relates to an electronic switch comprising a photosensitive semiconductor and a light source which, when actuated, illuminates the semiconductor and causes the latter to become conductive.
Photosensitive semiconductors are well known and need not be described in detail. The main characteristic of such semiconductors is their ability to pass from an electrically non-conductive and high resistance state to an electrically conductive and low resistance state when they are illuminated with light.
Materials presently used as or in industrial photosensitive semiconductors are for example : silicon, carbon, germanium, gallium arsenide, silicon carbide, cadmium selenide, cadmium sulphide, indium phosphide, and potassium phosphide. These prior art photosensitive seiniconductors can be used in various electronic devices, for example, in electronic switches, and are generally doped with "impurities" such as, for example cobalt, copper, chromium, gold, iron, oxygen, silver, and zinc.
Electronic switches comprising a photosensitive semiconductor are described, for example, in the following U.S. Pat. Nos.: 4,301,362; 4,347,437; 4,438,331; 4,490,709; 4,577,114 and 4,695,733. Various configurations of switches are described in these patents. They all comprise a light source and a photosensitive semiconductor provided with two spaced electrodes. The semiconductors are made of various materials and the light source is generally a laser.
When, for a given semiconductor, a certain bias voltage is applied across the electrodes of a photosensitive switch, the semiconductor will not permit the electrical current to pass between the electrodes and the switch will be in its "off" position, but when the light source projects light energy on to the area of the semiconductor located between the electrodes the semiconductor becomes electrically conductive and the switch will be in its "on" position. The main advantage of switches of this type is that they can switch an electrical current on or off very rapidly.
A disadvantage of known photosensitive switches and, in particular, of the switches disclosed in the above six U.S. patents is that they are only capable of switching electrical supplies which have voltages of a few kV, for example up to 3-5 kV, and thus cannot be used in electrical devices where a higher voltage is required.